Measuring pick-ups or load cells such as force pick-ups or load cells having a sensor body to which at least one strain gage is applied, are generally sensitive to variations in the load application conditions. Thus, the measuring characteristics of such pick-ups may change when the load application conditions change. For example, different measuring results may be obtained for the same applied load if even minor angular deviations occur in the direction of the load application such as an angular deviation from a vertical load application direction or in the point of load application. Other causes such as non-uniformities and non-symmetries in the construction of the sensor body and/or in the strain gage element or elements applied to the sensor body provide further sources for variations in the measuring characteristic of such pick-ups. These other causes are due to manufacturing tolerances which cannot be avoided for economic reasons.
In order to assure exact measuring results that are consistently repeatable, it is necessary to take steps that eliminate the possibly adverse influences of load application conditions that may vary due to the above mentioned causes. However, conventionally these steps generally have to be taken after the installation of the measuring pick-up for example in a scale in the manufacturing plant. Such conventionally necessary steps are bothersome because not only are they time consuming, they also require a complex correction procedure. It would be substantially easier to desensitize or tune pick-ups prior to their installation to make them less sensitive to varying load application conditions.
European Patent Publication EP-A 0,089,209 (Griffen et al.), published on Sep. 21, 1983, calls for the application of testing loads to a scale after the load receiving scale platform has been rigidly connected to the measuring pick-up and after the measuring pick-up has been rigidly connected with the scale base, whereby these testing loads are to be applied prior to any compensating steps, for example, in the form of material removals or resistor adaptations in the strain gages.
Japanese Patent Publication 62-107033 (Tanaka), published on Nov. 10, 1988, discloses a device with additional pick-up elements or strain gages positioned so that loads applied to the measuring pick-up caused by undesired moments or lateral forces, are picked-up and electronically corrected, whereby the measured value is corrected and a corrected load value is displayed. Even such an arrangement with additional pick-up elements or strain gages requires additional steps to be taken in the plant of the scale manufacturer.
Other attempts to minimize the effects of off-center load applications have been made, for example, by decoupling of lateral forces with the aid of roller bearings. These attempts also have their drawbacks, since such structural features with roller bearings are very expensive. Similar considerations apply to constructions in which the measuring or sensor body has a complicated and hence expensive geometry or where a multitude of pick-up elements, namely strain gages, are applied to the sensor body. All these conventional attempts aim at eliminating the effects of non-uniformities or non-symmetries in the sensor bodies or of angular or positional variations in the load applications or variations in the application of the strain gages to the sensor bodies. Incidentally, in this context, the term "measuring body" and the term "sensor body" are used as synonyms.